1. Field of the Invention
The invention relates to a ball screw device.
2. Description of the Related Art
A ball screw device described in Japanese Patent Application Publication No. 2010-71411 (JP 2010-71411 A) has a circulation path that provides communication between one end portion and the other end portion of a ball rolling path to allow balls to circulate along a raceway. The circulation path has a through-hole formed so as to pass through a peripheral wall of a ball nut in its axial direction, a feed-side communication passage that provides communication between one end of the through-hole and the one end portion of the ball rolling path, and a discharge-side communication passage that provides communication between the other end of the through-hole and the other end portion of the ball rolling path. The feed-side communication passage is formed in a feed-side deflector member attached to the peripheral wall of the ball nut, and the discharge-side communication passage is formed in a discharge-side deflector member attached to the peripheral wall of the ball nut.
The through-hole described in JP 2010-71411 A is formed through, for example, drilling. To facilitate the drilling, the through-hole needs to extend along the axial direction of the ball nut. However, if the through-hole is limited to the one that extends along the axial direction, the positions in the circumferential direction, where the paired deflectors (the feed-side deflector member and the discharge-side deflector member) are arranged, are limited. Therefore, in the ball screw device configured as described above, the adoptable number of turns is automatically limited to numbers of turns having a predetermined decimal fraction such as 7, that is, limited to, for example, 1.7 turns and 2.7 turns. Even if the theoretically required effective number of the turns of the ball screw device is, for example, 2.3, it is necessary to employ the ball screw device of which the effective number of the turns is 2.7. Therefore, there is a possibility that the ball screw device becomes larger than necessary in the axial direction.